Imaging target for photoconduction type image pickup device

ABSTRACT

An imaging target for a photoconduction type image pickup device, comprising a transparent face plate, a light-shielding material film provided on at least a part of the portion of the inner surface of the face plate excepting the effective imaging section of the face plate, a transparent conductive film provided on the face plate having the light-shielding material film thereon and a photoconductive film provided on the transparent conductive film, wherein a light-permeable protection film of a material non-corrodible to a treating solution corroding the photoconductive film is provided at least between the lightshielding material film and the transparent conductive film, the local concentration of an electric field of high intensity at the edge portion of the light-shielding material film being prevented and the reusing of the face plate and the light-shielding material film being enabled.

'llnited States Paten Suzuki Dec. 16, 1975 15 1 IMAGING TARGET FOR 3,519,866 7/1970 Leaman 313/65 A 3,772,552 11/1973 1411156111 313/329 x PHOTOCONDUCTION TYPE IMAGE PICKUP DEVICE Hirofumi Suzuki, Mobara, Japan Assignee: Hitachi, Ltd., Japan Filed: Jan. 21, 1974 Appl. No.: 434,780

Inventor:

Foreign Application Priority Data Feb. 9, 1973 Japan 48-15652 Feb. 9. 1973 Japan 48-15653 US. Cl 313/371; 313/386 Int. Cl. ..H01J 29/36; l-lOlJ 31/38 Field of Search 313/65 A, 386, 384, 390,

12/1966 Heagy ..313/385 12/1968 Bynum ..313/39O Primary ExaminerRobert Segal Attorney, Agent, or FirmCraig & Antonelli 57 ABSTRACT An imaging target for a photoconduction type image pickup device, comprising a transparent face plate, a light-shielding material film provided on at least a part of the portion of the inner surface of the face plate excepting the effective imaging section of the face plate, a transparent conductive film provided on the face plate having the light-shielding material film thereon and a photoconductive film provided on the transparent conductive film, wherein a light-permeable protection film of a material non-corrodible to a treating solution corroding the photoconductive film is provided at least between the light-shielding material film and the transparent conductive film, the local concentration of an electric field of high intensity at the edge portion of the light-shielding material film being prevented and the reusing of the face plate and the lightshielding material film being enabled.

24 Claims, 12 Drawing Figures .Patent Dec. 16, 1975 Sheet 1 of 3 FIG.|

US. Patent Dec. 16, 1975 Sheet20f3 3,927,340

FIG.6b

FIG.60

IMAGING TARGET FOR PHOTOCONDUCTION TYPE IMAGE PICKUP DEVICE ing member for picking up the reference level of dark current and to a target for a photoconduction type color image pickup device provided with such a lightshielding member and a color separation filter.

First, the term effective imaging section used throughout the specification is defined. In general, an area A, on a face plate of an image pickup device, in which the image of an object is formed on a photoconductive film on the face plate is smaller than an area B on the face plate scanned by an electron beam from an electron gun of the image pickup device and is larger than an area C on the face plate, the image in the area C being reproduced in a receiver or receiver tube. This area C is called effective imaging section.

In a typical photoconduction type image pickup device, e.g. a vidicon, the image of an object is formed through an optical system on a photoconductive film provided on the imaging target to convert the optical pattern to an electrical signal. The photoconductive film is usually formed of antimony trisulfide, lead oxide, cadmium selenide or selenium arsenide and each of the compounds has a characteristic that the dark current varies very much with variations in temperature. The dependence of the dark current on temperature is compensated for by providing a light-shielding portion, i.e., a dark leveler around the periphery of the effective imaging section of the photoconductive film, by scanning that portion of the photoconductive film which covers the dark leveler by an electron beam so as to obtain a signal corresponding to the dark current and by detecting the signal to control the target voltage. In such an image pickup device, a transparent conductive filmto take out the electrical signal is provided between the photoconductive film and the face plate and between the photoconductive film and the dark leveler. The transparent conductive film is a porous one made of tin oxide, indium oxide or their composite compound. Moreover, in a color image pickup device having a color separation filter, the color filter is generally provided between the substrate and the transparent conductive film.

In such image pickup devices as described above, a transparent conductive film and a photoconductive film are formed on a face plate provided with a dark leveler (and color separation filter) and then the characteristic of the effective imaging section of this face plate is measured. If the characteristic is not satisfactory, the photoconductive film on the face plate is removed by a treating solution such as acid or an alkaline solution and the face plate with the dark leveler (and the color separation filter) is reused. However, since the transparent conductive film is porous as mentioned above, the treating solution used to remove the photoconductive film reaches the dark leveler (and the color separation filter) lying beneath the transparent conductive film. Consequently, the solution may form pinholes in the dark leveler (and the color separation filter) or cause the peeling-off thereof to render the face plate unsuitable for reuse. Further, it is very difficult to remove from the face plate the dark leveler (and the color separation filter) damaged by the treating solution. Moreover, since the dark leveler has to be placed in position with a, high accuracy, the reforming of the dark leveler requires many elaborate measurements and adjustments. In addition, in the structure described above, the photoconductive film necessarily hasa relatively sharp. edge near the end of the dark leveler so that an electric field of high intensity concentrates at the edge portion, causing flaws and noise.

It is therefore one object of the present invention to provide a target for a photoconduction type image pickup device,.in which a photoconductive film can be removed without adversely affecting a transparent conductive film and a dark leveler (and a color separation filter) so that the face plate may lend itself readily to reuse.

Another object of the present invention is to provide a target for a photoconduction type image pickup device, which is free from the concentration of an electric field of high intensity to cause flaws and noise.

Yet another object of the present invention is to provide a target for a photoconduction type image pickup device, in which after removal of a photoconductive film another photoconductive film, can be re coated without reforming a new transparent conductive film and dark leveler (and color separation filter).

According to the present invention there is provided an imaging target for a photoconduction type image pickup device, comprising a transparent face plate, a light-shielding material film provided on at least a part of the portion of the inner surface of the face plate excepting the effective imaging section of the face plate, a transparent conductive film provided on said face plate having the light-shielding material film, a photoconductive film provided on the transparent conductive film, and a light-permeable protection film of a material non-corrodible to a treating solution corroding the photoconductive film, the light-permeable protection film being provided at least between the lightshielding material film and the transparent conductive film.

Other objects, features and advantages of the present invention will become apparent when reading the following detailed description in conjunction with the accompanying drawings, in which:

FIG. 1 schematically shows the principle of a photoconduction type image pickup device;

FIG. 2 is a front view of a target used in an image pickup device;

FIG. 3 is a cross section taken along line III-III in FIG. 2, which shows the structure of a conventional target;

FIG. 4 is a cross section as taken along line IV-IV in FIG. 2, which shows the structure of a target as one embodiment of the present invention;

FIG. 5 is a cross section as taken along line VV in FIG. 2, which shows the structure of a target as another embodiment of the present invention;

FIGS. 6a and 6b are front views of a target for an image pickup device according to the present invention, arranged in different manners;

FIG. 7 is a front view of a target for a color image pickup device;

FIG. 8 is a cross section taken along line VIII-VIII in FIG. 7, which shows the structure of a conventional target;

FIG. 9 is a cross section as taken along line IXIX in FIG. 7, which shows the structure of a target embodying the present invention; and

FIGS. a and 10b are fr'ont'views of a light-shielding part in the target for a color image pickup device embodying the present invention, arranged in different manners.

In FIG. 1 which illustrates the principle of a photoconduction type image'pickup device, the device includes an envelope 1 and an electron gun 2 is mounted at one end of the envelope 1. A transparent conductive film 4 and a photoconductive film 5 are provided on the inner surface of a face plate 3 mounted at the other end of the envelope 1. In operation, a light pattern from an object (not shown) is passed through an optical system 6 having a combination of lenses and imaged on the photoconductive film 5. The image formed on the film 5 is then scanned by an electron beam 7 emitted from the electron gun 2 and controlled by a focusing coil 8 and a deflection coil 9. Consequently, the image is delivered as an electrical signal from an output terminal 10. Reference numeral 11 indicates a light-shielding part called a dark leveler, which will be described later. The face plate 3, the dark leveler 11, the transparent conductive film 4 and the photoconductive film 5 constitute an imaging target. The photoconductive film 5 is usually made of antimony trisulfide, lead oxide, cadmium selenide or selenium arsenide. Each of the materials, however, has a characteristic that dark current varies very much with variations in temperature. Since the dark current can be varied by changing the target voltage in an image pickup device using antimony trisulfide as a photoconductive film, the variation in dark current due to temperature change is usually compensated for according to the following method. Namely, a light-shielding part, i.e., dark leveler 11, made of chromium, platinum, rhodium, palladium, carbon, manganese dioxide, or cadmium selenide is formed on the face plate 3, except the effective imaging section 12 of the plate 3 and then the transparent conductive film 4 and the photoconductive film 5 are formed over the dark leveler 11, as shown in FIGS. 2 and 3. With this structure, since the dark leveler ll completely blocks the light sent through the optical system 6, a signal corresponding to a dark current can be obtained each time the electron beam 7 scans that portion of the photoconductive layer 5 which lies on the dark leveler 11. Accordingly, dark current changing with temperature can be controlled so as to be kept constant by controlling thetarget voltage with the signal. In this case, a transparent conductive film 4 to be used as a signaling electrode is formed between the face plate 3 and the photoconductive film 5. The transparent conductive film 4 is made of tin oxide, indium oxide or their composite compound. The transparent film 4 must be porous irrespective of its material and, for example, when tin oxide is used, heat treatment at about 500C is needed while temperature of about 200C is needed for the heat treatment of an indium oxide film. Accordingly, the dark leveler 11 must withstand such temperatures during heat treatment. Further, in such an image pickup device as mentioned above, the characteristic of the device is measured after the photoconductive film 5 is vapor-deposited on the transparent conductive film 4 and if the characteristic is unsatisfactory, the photoconductive film 5 on the face plate 3 is removed away by an acid or alkaline solution to prepare the expensive face plate 3 for reuse.

However, since the transparent conductive film 4 is porous, the solution to corrode the photoconductive film 5 reaches the dark leveler 11 and forms there pinholes or peeling-off so that the face plate 3 can no longer be reused. It is very difficult to remove from the face plate the transparent conductive film and the dark leveler which are corroded by the solution. Moreover, the positioning of the dark leveler requires high accoracy and therefore many elaborate work steps. Further, with such a structure as mentioned above, the photoconductive film has a sharp edge at the end of the dark leveler and a high intensity electric field concentrates on the edge so that flaws and noise are often caused.

According to the present invention, these drawbacks are solved by providing a light-permeable protection film non-corrodible to a solution for removing the photoconductive film.

FIG. 4 shows an example of a target for an image pickup device embodying the present invention. As shown in FIG. 4, a light-permeable protection film 13 is coated on both a glass face plate 3 and a dark leveler l l and a transparent conductive film 4 is coated on the entire surface of the face plate 3 having'the dark leveler 11 and protection film 13. The protection film 13 is closely formed through sputtering, CVD (chemical vapor deposition) or vacuum deposition of glass or silicon dioxide. A photoconductive film -5 is formed on the transparent conductive film 4. By virtue of the light-permeable protection film 13 on both the face plate 3 and the dark leveler 11, the photoconductive film 5 can be easily removed by treating with a solution such as acid or alkaline solution. Since the protection film 13 is closely formed of glass or silicon dioxide non-corrodible to the solution, the solution cannot reach the dark leveler 11. Thus, the dark leveler 11 can be prevented from undesirably corroding during treatment for removing the photoconductive film 5 from the face plate 3. Moreover, since in this case the dark leveler 11 is completely protected, a photoconductive film can be formed anew without recoating a dark leveler and a transparent conductive film if sufficient cleaning is performed after the removal of the old photoconductive film for the reuse of the face plate. The lightpermeable protection film 13 formed on-the dark leveler 11 serves also to round the contour of the edge of the dark leveler so that the photoconductive film 5 also has a rounded edge which is free from the concentration of a high intensity electric field to cause flaws in the photoconductive film corresponding to the edge and electrical noise. Therefore, if the protection film 13 is so formed as to have an even surface or if the formed film 13 is artificially flattened by ion-etching or a chemical or mechanical polishing method, then the portion where the local concentration of an electric field of high intensity takes place can be eliminated so that the resultant flaws and noise are also eliminated.

FIG. 5 shows another embodiment of the present invention, similar to that shown in FIG. 4, in which the light-permeable protection film 13 is formed only on the dark leveler ll.

In the embodiments shown in FIGS. 4 and 5, the light-shielding part as dark leveler is so formed as to completely enclose the effective imaging section, but the present invention is by no means limited to those embodiments alone. For example, a stripe-shaped lightshielding part as a dark leveler may be horizontally or vertically arranged, as shown in FIGS. 6a and 6b, to

obtain the same effect.

The present invention can be embodied also in a target for a photoconduction type color image pickup device having a color separation filter, e.g. a stripeshaped color filter. In such a photoconduction type color image pickup device having a stripe-shaped color filter, for example the pattern formed through the optical system and the stripe-shaped color filter on the photoconductive film provided in an electron beam scanning section, is converted to an electrical signal. Recently, a single or double tube type color image pickup device using a color separation filter has found wide application in simple color cameras for industrial and domestic use.

FIGS. 7 and S are respectively a front view and a sectional view of a target for a conventional color image pickup device having a stripe-shaped color filter. The same reference numerals are applied to like parts or elements as in the preceding figures. A stripe-shaped color filter 14 is provided on the effective imaging section 12 of the face plate 3. The stripe-shaped color filter 14 is coated in such a manner that elements of filter components for special colors are provided parallel to one another along the vertical direction or a direction inclined therefrom or are provided in cross with one another. The characteristic of the target having such a structure as mentioned above is examined after the forming of the photoconductive film 5 and if the target proves to be unsatisfactory, the photoconductive film is removed by a solution to prepare the face plate for reuse. During the removing treatment, however, the stripe-shaped color filter as well as the dark leveler is corroded by the solution. Moreover, the photoconductive film has a sharp edge at the end of the color filter as well as at the end of the dark leveler and such a sharp edge is causative of the concentration of an electric field of high intensity.

FIG. 9 shows a target for a color image pickup device embodying the present invention. In FIG. 9, a lightpermeable protection film 13 is coated on both a stripeshaped color filter 14 and a dark leveler 11, a transparent conductive film 4 is formed on the protection film l3, and a photoconductive film is formed on the transparent conductive film 4. With this structure, the photoconductive film 5 can be easily removed by treating with a solution such as acid or alkaline solution, without injuring the color filter l4 and the dark leveler 11. And the light-permeable protection film 13, closely formed of a material such as glass or silicon dioxide incorrodible to the treating solution, completely prevents the solution from reaching the color filter l4 and the dark leveler 11. Moreover, since the protection film 13 makes the edges of the dark leveler l1 and the stripe-shaped color filter l4 round-contoured, portions where the concentration of an electric field of high intensity causative of flaws and noise takes place can be eliminated. Therefore, if the protection film 13 is so formed as to have an even surface or if the formed film 13 is artificially flattened by ion-etching or a chemical or mechanical polishing method, then the portion where the local concentration of an electric field of high intensity takes place can be eliminated so that the associated flaws and noise are also eliminated.

In the embodiment in FIG. 9, the light-shielding part as a dark leveler is so formed as to completely encircle the effective imaging section but the present invention is by no means limited to this embodiment alone. For example, a stripe-shaped dark leveler may be arranged along only the horizontal or vertical deflection direction, as shown in FIGS. 10a and 10b, to obtain the same effect. Moreover, in the above embodiment, the lightpermeable protection film covers the stripe-shaped color filter, the dark leveler and the other portions of the face plate but it is only necessary for the protection film to cover at least the color filter and the dark leveler.

As described above, according to the present invention, a light-permeable protection film is coated on the dark leveler (and the color separation filter) provided on the face plate so that the dark leveler (and the color separation filter) can be prevented from being corroded by the etching solution to etch away the photoconductive film during the treatment to prepare the unsatisfactory face plate for reuse. Therefore, after the photoconductive film has been removed, a new photoconductive film can be formed without the recoating of a transparent conductive film which was necessary in the prior art. Moreover, since the protection film serves to flatten the surface contours of the photoconductive layer, the local concentrations of higher intensity field causative of flaws and noise can be eliminated.

What is claimed is:

1. An imaging target for a photoconduction type image pickup device, comprising a transparent face plate, a light-shielding material film provided on at least a part of the portion of the inner surface of said face plate excepting the effective imaging section of said face plate, a transparent conductive film provided over said face plate and said light-shielding material film, a photoconductive film provided on said transparent conductive film at least over the effective imaging section of said face plate, and a light-permeable protection film of a material non-corrodible to a treating solution corroding said photoconductive film, said light-permeable protection film being provided at least between said light-shielding material film and said transparent conductive film and being provided directly on said light shielding material film.

2. An imaging target as claimed in claim 1, further comprising a color separation filter provided on the inner surface of said face plate and in said effective imaging section, said light-permeable protection film being provided directly on said color filter.

3. An imaging target as claimed in claim 1, wherein said light-permeable protection film covers the edge portion of said light-shielding material film to prevent the local concentration of an electric field of high intensity at said edge portion.

4. An imaging target as claimed in claim 2, wherein said light-permeable protection film covers the edge portion of said color separation filter to prevent the local concentration of an electric field of high intensity at said edge portion.

5. An imaging target as claimed in claim 1, wherein the outer surface of said light-permeable protection film is substantially flat.

6. An imaging target as claimed in claim 1, wherein said light-permeable protection film is closely formed of glass.

7. An imaging target as claimed in claim 1, wherein said light-permeable protection film is closely formed of silicon dioxide.

8. An imaging target for a photoconduction type image pickup device, said target comprising a transparent face plate; a light-shielding material film having a first and a second surface, said first surface contactlflg at least a part of the portion of the inner surface of said face plate excepting the effective imaging section of said face plate; a light-permeable protection film having a first and a second surface, said first surface of said light-permeable protection film contacting at least said second surface of said light-shielding material film; a transparent conductive film having a first and a second surface and being disposed at least over the effective imaging section of said face plate, said first surface of said transparent conductive film contacting at least said second surface of said light-permeable protection film; and a photoconductive film formed on said second surface of said transparent conductive film; said lightpermeable protection film comprising a material which is not corroded by a treating solution corroding said photoconductive film.

9. An imaging target as defined in claim 8, wherein said light permeable protection film lies between said transparent conductive film and said transparent face plate in said effective imaging section, whereby said first surface of said light permeable protection film contacts said inner surface of said face plate in said effective imaging section.

10. An imaging target as defined in claim 8, wherein said first surface of said transparent conductive film also contacts said inner surface of said face plate in said effective imaging section.

11. An imaging target as defined in claim 8, further comprising a color separation filter provided on said inner surface of said face plate in said effective imaging section, said first surface of said light-permeable protection film also contacting said color separation filter.

12. An imaging target as defined in claim 11, wherein said light-permeable protection film covers the edge portion of said color separation filter to prevent local concentration of an electric field of high intensity at said edge portion.

13. An imaging target as defined in claim 8, wherein said light-permeable protection film covers the edge portion of said light-shielding material film to prevent local concentration of an electric field of high intensity at said edge portion.

. 14. An imaging target as defined in claim 8, wherein said light-permeable protection film is closely formed of glass.

15. An imaging target as defined in claim 8, wherein said light-permeable protection film is closely formed of silicon dioxide.

16.'An imaging target as defined in claim 8, wherein said treating solution is made from an acid or an alkaline solution.

17. An imaging target as defined in claim 8, wherein said light-shielding material film is stripe-shaped.

18. An imaging target as defined in claim 8, wherein said light-shielding material film is stripe-shaped and lies along the vertical deflection direction of said device.

19. An imaging target as defined in claim 11, wherein said light-shielding material film is stripe-shaped and lies along the horizontal deflection direction of said device.

20. An imaging target as defined in claim 11, wherein said light-shielding material film is stripe-shaped and.

21. An imaging target as defined in claim 1 wherein said transparent conductive film is continuous at least in the area of said effective imaging section.

22. An imaging target as defined in claim 8 wherein said transparent conductive film is continuous at least in the area of said effective imaging section.

23. An imaging target as defined in claim 17, wherein said light permeable protection film lies between said transparent conductive film and said transparent face plate in said effective imaging section, whereby said first surface of said light permeable protection film contacts said inner surface of said face plate in said effective imaging section.

24. An imaging target as defined in claim 17, wherein said first surface of said transparent. conductive film also contacts said inner surface of said face plate in said effective imaging section. 

1. An imaging target for a photoconduction type image pickup device, comprising a transparent face plate, a light-shielding material film provided on at least a part of the portion of the inner surface of said face plate excepting the effective imaging section of said face plate, a transparent conductive film provided over said face plate and said light-shielding material film, a photoconductive film provided on said transparent conductive film at least over the effective imaging section of said face plate, and a light-permeable protection film of a material non-corrodible to a treating solution corroding said photoconductive film, said light-permeable protection film being provided at least between said light-shielding material film and said transparent conductive film and being provided directly on said light shielding material film.
 2. An imaging target as claimed in claim 1, further comprising a color separation filter provided on the inner surface of said face plate and in said effective imaging section, said light-permeable protection film being provided directly on said color filter.
 3. An imaging target as claimed in claim 1, wherein said light-permeable protection film covers the edge portion of said light-shielding material film to prevent the local concentration of an electric field of high intensity at said edge portion.
 4. An imaging target as claimed in claim 2, wherein said light-permeable protection film covers the edge portion of said color separation filter to prevent the local concentration of an electric field of high intensity at said edge portion.
 5. An imaging target as claimed in claim 1, wherein the outer surface of said light-permeable protection film is substantially flat.
 6. An imaging target as claimed in claim 1, wherein said light-permeable protection film is closely formed of glass.
 7. An imaging target as claimed in claim 1, wherein said light-permeable protection film is closely formed of silicon dioxide.
 8. An imaging target for a photoconduction type image pickup device, said target comprising a transparent face plate; a light-shielding material film having a first and a second surface, said first surface contacting at least a part of the portion of the inner surface of said face plate excepting the effective imaging section of said face plate; a light-permeable protection film having a first and a second surface, said first surface of said light-permeable protection film contacting at least said second surface of said light-shielding material film; a transparent conductive film having a first and a second surface and being disposed at least over the effective imaging section of said face plate, said first surface of said transparent conductive film contacting at least said second surface of said light-permeable protection film; and a photoconductive film formed on said second surface of said transparent conductive film; said light-permeable protection film comprising a material which is not corroded by a treating solution corroding said photoconductive film.
 9. An imaging target as defined in claim 8, wherein said light permeable protection film lies between said transparent conductive film and said transparent face plate in said effective imaging section, whereby said first surface of said light permeable protection film contacts said inner surface of said face plate in said effective imaging section.
 10. An imaging target as defined in claim 8, wherein said first surface of said transparent conductive film also contacts said inner surface of said face plate in said effective imaging section.
 11. An imaging target as defined in claim 8, further comprising a color separation fiLter provided on said inner surface of said face plate in said effective imaging section, said first surface of said light-permeable protection film also contacting said color separation filter.
 12. An imaging target as defined in claim 11, wherein said light-permeable protection film covers the edge portion of said color separation filter to prevent local concentration of an electric field of high intensity at said edge portion.
 13. An imaging target as defined in claim 8, wherein said light-permeable protection film covers the edge portion of said light-shielding material film to prevent local concentration of an electric field of high intensity at said edge portion.
 14. An imaging target as defined in claim 8, wherein said light-permeable protection film is closely formed of glass.
 15. An imaging target as defined in claim 8, wherein said light-permeable protection film is closely formed of silicon dioxide.
 16. An imaging target as defined in claim 8, wherein said treating solution is made from an acid or an alkaline solution.
 17. An imaging target as defined in claim 8, wherein said light-shielding material film is stripe-shaped.
 18. An imaging target as defined in claim 8, wherein said light-shielding material film is stripe-shaped and lies along the vertical deflection direction of said device.
 19. An imaging target as defined in claim 11, wherein said light-shielding material film is stripe-shaped and lies along the horizontal deflection direction of said device.
 20. An imaging target as defined in claim 11, wherein said light-shielding material film is stripe-shaped and.
 21. An imaging target as defined in claim 1 wherein said transparent conductive film is continuous at least in the area of said effective imaging section.
 22. An imaging target as defined in claim 8 wherein said transparent conductive film is continuous at least in the area of said effective imaging section.
 23. An imaging target as defined in claim 17, wherein said light permeable protection film lies between said transparent conductive film and said transparent face plate in said effective imaging section, whereby said first surface of said light permeable protection film contacts said inner surface of said face plate in said effective imaging section.
 24. An imaging target as defined in claim 17, wherein said first surface of said transparent conductive film also contacts said inner surface of said face plate in said effective imaging section. 